Hemolytic parasites affect survival in migrating red-tailed hawks

Area of Science:

• Avian ecology
• Wildlife physiology
• Parasitology

Background:

• Migratory birds face numerous survival challenges, including parasites and energy demands.
• Understanding how individual health impacts population dynamics is vital for conservation.
• Linking physiological condition, disease, and survival in migratory species is challenging.

Purpose of the Study:

• To investigate the relationship between physiological condition, hemoparasite infection, and survival in migrating red-tailed hawks.
• To assess the influence of parasites on individual survival during migration.
• To explore potential trade-offs between survival and immune function.

Main Methods:

• Analysis of blood smears for hemoparasite presence and abundance in 353 red-tailed hawks (2004-2018).
• Measurement of physiological condition using scaled-mass index and heterophil/leukocyte (H/L) ratio.
• Assessment of immune defenses including hemolytic-complement activity and bacteria-killing ability.

Main Results:

• Hemoparasites (Haemoproteus, Leucocytozoon) were found in 39.4% of hawks.
• H/L ratio was negatively correlated with scaled-mass index; adults had higher H/L ratios than juveniles.
• Haemoproteus parasitemia was negatively associated with individual survival, indicating increased mortality risk.

Conclusions:

• Haemosporidian parasite infection, specifically Haemoproteus, significantly impacts the survival of individual red-tailed hawks during migration.
• Parasite load, not immune defense trade-offs, appears to be a key factor affecting survival in this migratory population.
• Findings highlight the importance of considering parasite-host interactions in avian migration and conservation strategies.